Nitroalkanes are an essential stabilizing ingredient employed in 1,1,1-trichloroethane when it is used in vapor degreasing and cold cleaning. All manufacturers throughout the world add nitromethane and/or nitroethane to their commercial 1,1,1-trichloroethane-based solvents. Normally nitro-paraffins are manufactured by a vapor phase nitration of the alkane with either nitric acid or NO.sub.2. There is a mixture of products formed due to carbon-carbon scission. Thus, for example, when propane is nitrated, the products include 1-nitropropane, 2-nitropropane, nitroethane and nitromethane. Because of the oxidative conditions other oxygen containing compounds are also produced, e.g. aldehydes, acids and carbon oxides. Patents disclosing such a process are U.S. Pat. Nos. 2,844,634 and 2,905,724.
Improvements in these vapor phase nitrations are claimed by employing the nitric acid or nitrogen oxides together with oxygenated sulfur compounds, e.g. SO.sub.2, H.sub.2 SO.sub.4, (U.S. Pat. No. 3,272,874) and by conducting the nitration in the presence of ozone (U.S. Pat. No. 3,113,975).
Other processes involve nitration of paraffins by nitrogen peroxide (NO.sub.2).sub.2 in the presence of oxygen (air) under pressure at 150.degree.-330.degree. C. (U.S. Pat. No. 3,780,115); reacting an olefin with nitric acid in the presence of a lower aliphatic monocarboxylic acid anhydride to produce a nitroester, subsequently reducing it with an alkali borohydride to form the nitroalkane (U.S. Pat. No. 3,706,808) and reacting organic amines with ozone (U.S. Pat. No. 3,377,387).
Another process, the subject of my copending application (with another) Ser. No. 211,017, filed Nov. 28, 1980, now abandoned, is an improvement which reduces the amount of by-products and obtains improved yields of the desired products by the nitrating of paraffins with nitric acid at lower temperatures and pressures in the presence of high intensity light.
In yet another improved vapor phase process methane or ethane is reacted with nitric acid in the presence of an inert diluent gas at high temperatures, &gt;300.degree. C., over a catalyst, e.g. SrCl.sub.2 on a low surface area alumina. This is disclosed in my copending application, Ser. No. 352,506, filed Feb. 25, 1982.
The present invention is a departure from known methods in that it employs the reaction of methanol with nitric acid, or NO.sub.2 gas, in the vapor phase over a catalyst in a fixed bed.